Gosh there are some cynics here! Given that a lot of people meet their life partners through work, I don't think that this is any different. The risks are always there but so are the potential rewards.
To be honest, my main objection here is one of an imbalance of power.
As a landlord you have the control over a other person's shelter.
You must always exercise any form of legal power with the greatest of care and responsibility.
Assuming you are no Adonis, the reasonable assumpton by a court, should your tenant press a complaint, would be that you had committed a sex crime using duress.
You really don't want the title of sex offender on your file.
The title of the thread suggests it's not "love at first sight" rather just a lusty desire so I agree with those suggesting you avoid a tryst with your tenant. It's not likely to end well and at worst it could be used against you in the future and as McDuck suggests it could get really bad.